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Uncle Ben
01-17-2008, 02:44 PM
Soooooooo...since I was playing hookie during Groucho's first class I now seek on-line education. :rolleyes:

Right now when I key up on lets say 145.145 (tone set at 107.2), the transmit frequency jumps to 144.545. Does this mean I'm running Duplex? If that is true then if I wanted to stay Simplex is it just a matter of disabling the freq shift?

:confused: :zilla:

Shark Bait
01-17-2008, 02:58 PM
It has to be that way for the repeater to work. You will be simplex when not tuned to a repeater frequency. 146.520 is a standard simplex frequency. I actually raised someone on that frequency on my way down to Ouray this past summer. He was quite surprised. I don't think we were even 10 miles apart.

Romer
01-17-2008, 03:01 PM
Thats still not called Duplex is it Chris?

Uncle Ben
01-17-2008, 03:05 PM
It has to be that way for the repeater to work. You will be simplex when not tuned to a repeater frequency. 146.520 is a standard simplex frequency. I actually raised someone on that frequency on my way down to Ouray this past summer. He was quite surprised. I don't think we were even 10 miles apart.

Ahhh....I'm beginning to understand....that has had me :confused: for a while. Back to my question.....if I turn off my freq shift technically I can be simplex on 145.145 without hitting the repeater...correct?

Uncle Ben
01-17-2008, 03:07 PM
Thats still not called Duplex is it Chris?

according to what I understand....:rolleyes:.....if you transmit on a differant freq than you recieve that IS duplex..

Shark Bait
01-17-2008, 03:17 PM
Ahhh....I'm beginning to understand....that has had me :confused: for a while. Back to my question.....if I turn off my freq shift technically I can be simplex on 145.145 without hitting the repeater...correct?

No. I believe 145.145 is the output frequency. I'm not sure if the frequency shift (of 600 kHz for 2m according to my book) occurs automatically from the radio when you press the talk button, if you've entered the PL tone for that frequency.
according to what I understand....:rolleyes:.....if you transmit on a differant freq than you recieve that IS duplex..

In reading my book, I guess it is considered Duplex.

Uncle Ben
01-17-2008, 03:18 PM
BTW I am just using 145.145 as an example as I know it would be socially unacceptable to congest a repeater freq like that....

Hulk
01-17-2008, 03:39 PM
I think some of the band is designated for repeaters and other parts for simplex. So you wouldn't try to run simplex on 145.145, even if there wasn't a repeater set up in your area. IIRC, this varies by state depending on the local band plan.

Hulk
01-17-2008, 03:40 PM
BTW I am just using 145.145 as an example as I know it would be socially unacceptable to congest a repeater freq like that....

It wouldn't interfere with the repeater operation unless you were broadcasting the tone anyway.

Uncle Ben
01-17-2008, 03:50 PM
It wouldn't interfere with the repeater operation unless you were broadcasting the tone anyway.

Ahhhhhh....there's another piece of the pie! Thanks!

DaveInDenver
01-17-2008, 03:52 PM
No, it's sort of duplex (called half duplex). Duplex means that the channel is two directional at the same time. Like your telephone, you both can talk and hear at the same time. With a repeater, you have an input frequency and a retransmitted frequency. But when you key the mic, you can't hear anyone else on the repeater. So you are picking between one or the other half of the duplex channel. If you have a dual VFO radio, then you could tune both sides to the repeater output (say 145.145) and when you transmit on one side, the other would still listen. This causes feedback, though, if you have the volume up. But if you wore headphones, then you could hear your transmission and would be in full duplex with the repeater (not with everyone else using the repeater, though). The whole system, input freq., output freq. and all the gear comprises a duplex repeater. But each user station is only a half duplex since it must chose to either TX or RX and can't do both at the same time (with the exception of the two tuner radio example).

The reason you have two frequencies is that for the repeater to both TX and RX in real time it must transmit on a difference frequency than it's listening. If the repeater used the same frequency, then in real time it would always hear itself. Even with a shift you still have to isolate one side from the other to keep from causing problems. This is done with a duplexer with a single antenna.

It is possible to do a single frequency repeater (called technically a simplex repeater). This is usually done with a time delay. So the repeater listens until you are done talking, recording your transmission, and then rebroadcasts it after you are done. These are often also called parroting repeaters. These are used often for GMRS repeaters more than ham.

Uncle Ben
01-17-2008, 03:59 PM
DaveinDenver = http://www.dinicartoons.com/forum/images/smilies/Star_Wars/yoda4.gif
.......but the really spooky part is I'm starting to understand what he's saying! :eek: :lmao: ;)

DaveInDenver
01-17-2008, 04:11 PM
DaveinDenver = http://www.dinicartoons.com/forum/images/smilies/Star_Wars/yoda4.gif
.......but the really spooky part is I'm starting to understand what he's saying! :eek: :lmao: ;)
I figure I've learned a ton of gearhead junk from you guys, might as well not pull any punches and give you the straight dope. I could just say "The whizbang transmit thingie doesn't play nicely with the gizmo receive doohicky", but what good would that do? You're no worse off if it all goes over your head and probably just a little smarter than your average ham if some of it makes sense.

Groucho
01-17-2008, 06:38 PM
Soooooooo...since I was playing hookie during Groucho's first class I now seek on-line education. :rolleyes:

Right now when I key up on lets say 145.145 (tone set at 107.2), the transmit frequency jumps to 144.545. Does this mean I'm running Duplex? If that is true then if I wanted to stay Simplex is it just a matter of disabling the freq shift?

:confused: :zilla:

*EDIT* I started this at 2:17 and got called away, then finished it before realizing all the other posts!

Silly billy! The class is in February, not January!

In order to utilize one antenna for the actual repeater site on the mountain, the radios there use what is called a duplexer. This is a device that, simply put, makes it so that the electronics don't fry in the repeater receiver when the transmit is transmitting.

Most of the repeaters in use that are not linked to other repeaters(we'll go over all this in the class) operate on what is called "full duplex". Full Duplex is a communications mode in which a radio can transmit and receive at the same time by using two different frequencies. This difference in frequency is called a "shift". Standard VHF shift is +/-600 KhZ, depending on where the frequency is in the band.

The opposite of this is what Chris was saying, Simplex. It uses no offset "shift ", so all transmitting and recieving has to be done separate of the other. Simplex is what is used on CB(AM).

Got it?

Groucho
01-17-2008, 06:44 PM
It wouldn't interfere with the repeater operation unless you were broadcasting the tone anyway.

Correct, it wouldn't interfere with the repeater operation, however, folks near to your location will hear you and the repeater and it might be a little confusing.

corsair23
01-17-2008, 07:02 PM
DaveinDenver = http://www.dinicartoons.com/forum/images/smilies/Star_Wars/yoda4.gif
.......but the really spooky part is I'm starting to understand what he's saying! :eek: :lmao: ;)


Glad you do...My head hurts now...:hill: